Establish whether the system operated
Operating history during or after the event changes the migration hypothesis and what should be inspected.
Fire & Smoke · HVAC + Concealed Paths
Smoke can move with pressure, convection and building systems—so the visible room boundary is not always the migration boundary.
HVAC and concealed spaces should be investigated from evidence, not automatically declared contaminated or clean.
Inspect accessible evidence points
Returns, supplies, filters, accessible duct surfaces and blower components can provide evidence of system involvement.
Treat HVAC as a possible continuing source
When contamination is actually present, running the system can redistribute residue or odor after surrounding areas are cleaned.
Map non-HVAC pathways too
Stairs, shafts, pipe penetrations, electrical openings, ceiling voids and wall cavities can connect areas.
Respect licensing boundaries
Disassembly, electrical work, mechanical repair and regulated HVAC cleaning belong with qualified providers where required.
Verification rule: the endpoint is not “a method was applied.” The endpoint is whether the retained material, connected pathway and surrounding area have been re-checked for remaining residue, odor, damage and recontamination.